Guide star on edge of field
Joel Short
Dale Ghent
> On Jan 21, 2021, at 10:43, Joel Short <buckeyes...@gmail.com> wrote:
>
> I have noticed that when PHD2 automatically chooses a guide star it is almost always on the very edge of the OAG field of view. This hasn't been much of an issue for my refractors, but I now have a 12.5" iDK (f6.7 FL=2128mm) and there are far fewer stars to to choose from.
> Almost always, there are stars in the middle of the field that have a good profile for guiding but are never chosen by PHD2. Any tips for adjusting how PHD2 automatically chooses a a guide star?
In NINA, we allow the user to set the guide frame ROI in terms of percentage of the full guide camera frame size, so the ROI is always centered on the actual center of the camera's sensor, but it still allows the user to shrink the size of the image and effectively force PHD to consider stars more towards the center of the sensor and blocks off any that are at the physical edge of it. The app which controls PHD2 over the API would need to support calling find_star this way (as well as getting the sensor's dimensions by calling get_camera_frame_size first).
A better solution would be for PHD2 to derive a list of candidate guide stars and the ones that are closer to the center of the frame carry a higher weight when PHD2 decides which one to use.
/dale
bw_msgboard
It doesn’t matter where the star is in the field – it won’t get lost just because it’s near the edge. To get the best results from auto-find, you should do the following:
- Set the saturation level = the largest ADU your camera can return
- Set the min-HFD level = the smallest usable star size based on experience or measurements with your system
- Use a dark frame that is reasonably current and is a reasonable representation of your current sensor performance
If you want us to explain a single auto-find result that you’re not happy with, you need to send a debug log file and a specific time when you got the result and why you’re not happy with it. Poring through logs looking at single star-find results is time-consuming and tedious. FWIW, I run a configuration much like yours in a remote observatory and I’ve never had the auto-find function fail to find an acceptable guide star and produce good guiding results – nearly 2 years of operation with an emphasis on imaging galaxies.
Bruce
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bw_msgboard
candidate stars can be all over the field of view and their position doesn't
matter. What does matter is SNR and that's the property used for weighting.
I don't really see the point of worrying about the location in the field.
If the edge stars are affected by poor optical quality, that should be
reflected in their SNR values.
Bruce
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Brian Valente
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Richard Beck
Joel Short
bw_msgboard
The data being returned by your camera driver will be 16-bit – the pixel values are just scaled up from the internal 12-bit electronics. So you should choose a value of 65000 or so. That’s true for all these guide cameras – the interface is either 8-bit or 16-bit. If you were running with 255, that’s probably your problem right there.
Bruce
From: open-phd...@googlegroups.com [mailto:open-phd...@googlegroups.com] On Behalf Of Joel Short
Sent: Thursday, January 21, 2021
8:40 AM
To: Open PHD Guiding
Subject: Re: [open-phd-guiding] Guide star on edge of field
Bruce, I was really just looking for some guidance, which you provided.
I don't have empirical proof, but the edge stars seem to be more diffuse and the subsequent guiding seems to wobble more than stars that are more tight toward the middle of the FOV.
1. Somehow the saturation level was set at 255. I have a 12bit camera so I changed that to 4096.
2. I have the min-HFD level set to 1.3
3. I use a dark library that is fresh.
4. I have been using multi-star guiding since it came out and I have seen a slight improvement.
joel
On Thursday, January 21, 2021 at 10:23:53 AM UTC-6 bw_m...@ wrote:
It doesn’t matter where the star is in the field – it won’t get lost just because it’s near the edge. To get the best results from auto-find, you should do the following:
1. Set the saturation level = the largest ADU your camera can return
2. Set the min-HFD level = the smallest usable star size based on experience or measurements with your system
3. Use a dark frame that is reasonably current and is a reasonable representation of your current sensor performance
If you want us to explain a single auto-find result that you’re not happy with, you need to send a debug log file and a specific time when you got the result and why you’re not happy with it. Poring through logs looking at single star-find results is time-consuming and tedious. FWIW, I run a configuration much like yours in a remote observatory and I’ve never had the auto-find function fail to find an acceptable guide star and produce good guiding results – nearly 2 years of operation with an emphasis on imaging galaxies.
Bruce
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Joel Short
Dale Ghent
Understood about multi-star. Although ROI isn't a fix for this situation, I think we've seen some users run into situations where the star that was auto-selected was so close to the edge of the frame that it fell off later on in the session due to dithering. I think the prospect of this happening is what makes some users curl their toes a little when a star so close to the edge is selected.
Will multi-star pick a replacement and carry on with life if such a thing were to happen under its watch?
bw_msgboard
Hi Richard. You’re using that UI field correctly but it also sounds like you know what you’re doing. We put it in the dev build to see how things go and we haven’t added it to the documentation yet. What we have to constantly worry about is people fat-fingering the user interface or entering values that make no sense and thus finding no stars to use. It’s a fine line to walk. As you’ve seen, the values are very dependent on the properties of the guiding gear and we have to assume the user has otherwise set things up correctly with star-saturation level, min-HFD, focus, etc. The default value of 6 is based on photometric theory but it can be too low for many setups.
Bruce
From:
open-phd...@googlegroups.com [mailto:open-phd...@googlegroups.com] On Behalf Of Richard Beck
Sent: Thursday, January 21, 2021
8:31 AM
To: Open PHD Guiding
Subject: Re: [open-phd-guiding]
Guide star on edge of field
Bruce,
What about "Minimum star SNR for AutoFind"? I had some very low SNR stars selected and had lost stars. Increasing this value seemed to help.
The stars that seemed the best have SNRs in the 30s and 40s. I set this at 20 and seemed to have better results. Is there documentation on this parameter that I must have missed?
On Thursday, January 21, 2021 at 10:23:53 AM UTC-6 bw_m...@earthlink.net wrote:
It doesn’t matter where the star is in the field – it won’t get lost just because it’s near the edge. To get the best results from auto-find, you should do the following:
1. Set the saturation level = the largest ADU your camera can return
2. Set the min-HFD level = the smallest usable star size based on experience or measurements with your system
3. Use a dark frame that is reasonably current and is a reasonable representation of your current sensor performance
If you want us to explain a single auto-find result that you’re not happy with, you need to send a debug log file and a specific time when you got the result and why you’re not happy with it. Poring through logs looking at single star-find results is time-consuming and tedious. FWIW, I run a configuration much like yours in a remote observatory and I’ve never had the auto-find function fail to find an acceptable guide star and produce good guiding results – nearly 2 years of operation with an emphasis on imaging galaxies.
Bruce
From: open-phd...@googlegroups.com [mailto:open-phd...@googlegroups.com] On Behalf Of Joel Short
Sent: Thursday, January 21, 2021 7:44 AM
To: Open PHD Guiding
Subject: [open-phd-guiding] Guide star on edge of field
I have noticed that when PHD2 automatically chooses a guide star it is almost always on the very edge of the OAG field of view. This hasn't been much of an issue for my refractors, but I now have a 12.5" iDK (f6.7 FL=2128mm) and there are far fewer stars to to choose from.
Almost always, there are stars in the middle of the field that have a good profile for guiding but are never chosen by PHD2. Any tips for adjusting how PHD2 automatically chooses a a guide star?
I'm not sure it helps in this case, but here is my last guide log: https://openphdguiding.org/logs/dl/PHD2_logs_HLtj.zip
It may not be helpful because I was doing repeated autofocus runs to determine filter offsets.
joel
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Joel Short
bw_msgboard
of dithering. But if you're dealing with a sloppy setup, the guide star
could be lost for that reason. The desired solution in all these cases -
and I'm specifically talking about apps like NINA - is for the imaging app
to take the required recovery action. That means pausing the sequence,
re-issuing the auto-find/start-guiding, plate-solving, and re-centering if
necessary. Anything less than that is pretty much just praying for rain
IMO.
1E95B244606%40elemental.org.
Brian Valente
To view this discussion on the web visit https://groups.google.com/d/msgid/open-phd-guiding/117ea9ca-4a6d-4472-86ec-ef4649d68c5en%40googlegroups.com.
bw_msgboard
I generally set it to less than the theoretical max just for some headroom. The star brightness fluctuates between frames so you could see the max-ADU hit the theoretical maximum sporadically. But it’s not real important, the big issue is 255 vs 65K.
Bruce
From:
open-phd...@googlegroups.com [mailto:open-phd...@googlegroups.com] On Behalf Of Brian Valente
Sent: Thursday, January 21, 2021
8:29 AM
To: Open PHD Guiding
Subject: Re: [open-phd-guiding]
Guide star on edge of field
Bruce just a quick clarifying question:
>>>Set the saturation level = the largest ADU your camera can return
Do you set it to the absolute max, or slightly under that?
For 16-bit camera the max adu would be 65536
On Thu, Jan 21, 2021 at 8:23 AM bw_msgboard <bw_m...@earthlink.net> wrote:
It doesn’t matter where the star is in the field – it won’t get lost just because it’s near the edge. To get the best results from auto-find, you should do the following:
1. Set the saturation level = the largest ADU your camera can return
2. Set the min-HFD level = the smallest usable star size based on experience or measurements with your system
3. Use a dark frame that is reasonably current and is a reasonable representation of your current sensor performance
To view this discussion on the web visit https://groups.google.com/d/msgid/open-phd-guiding/CAJa45i45rn_Eqd5pRDfTju-u8Cre-1h%2BQwaRvdPxNzyrOERBNQ%40mail.gmail.com.
